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Supporting Information

Graphene Encapsulated Metallic State Ce2Sn2O7 as a Novel Anode Material for Superior

Lithium-Ion Batteries and Capacitors

Qiong Wu†, Yajin Liu†, Heng-guo Wang*,†,‡, Jianhua Hou*,†,‡, Yanhui Li†,‡, and Qian Duan*,†,‡

†School of Materials Science and Engineering, Changchun University of Science and

Technology Changchun, 130022, China

‡Engineering Research Center of Optoelectronic Functional Materials, Ministry of Education

Changchun, 130022, China

E-mail address: wanghengguo@cust.edu.cn (H. G. Wang) : houjh163@163.com (J. H. Hou);

duanqian88@hotmail.com (Q. Duan)

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2020

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Experimental Section

Materials: K2SnO3•3H2O (Aladdin Reagent, AR), Ce(NO3)3•6H2O (Beijing Chemical Works),

NaOH (Beijing Chemical Works), Polyvinylidene Fluoride (PVDF, DuPont Company, 99.9%),

Acetylene black (Hong-Xin Chemical Works), N-methyl-2-pyrrolidinone (NMP, Aladdin

Reagent, AR), Separator (polypropylene film, Celgard 2400), Commercial activated carbon

(AC, Aladdin Reagent), Deionized water (Laboratory preparation). Graphite oxide (GO) was

produced from natural graphite flakes by a modified Hummers method.1

Characterizations: The microstructures of the nanomaterials were observed by scanning

electron microscopy (SEM Hitachi S-4800) and transmission electron microscope (TEM)

recorded on a Tecnai. The crystal phases were evaluated by X-ray diffraction (XRD) patterns

recorded on a Rigaku-Dmax 2500 diffractometer with Cu Ka radiation. Thermogravimetric

analysis (TGA) was performed on a TA SDT 2960 simultaneous thermal analyzer between 25

and 1000 °C at a heating rate of 10 °C min-1 in Air. The specific surface areas of the powders

were calculated from a Brunauer Emmett Teller (BET) analysis of the nitrogen adsorption and

desorption measurements (Tristar 3000). X-ray photoelectron spectroscopy (XPS) analysis was

conducted with ESCALAB MK II X-ray instrument to analyze the composition of the

nanomaterials.

Computational details: The density functional theory (DFT) calculations were employed the

linear combination of the atomic orbital and spin-unrestricted methods and implemented in the

Dmol3 package. The generalized gradient approximation (GGA) in PBE functional form

together with an all-electron double numerical basis set with polarization function (DNP) was

adopted. In calculating the density of states (DOSs) and band structures, a denser k-point mesh

(4 × 4 × 4) was used. Electronic convergence was set to 10-6 eV, while atomic positions were

optimized until the final forces were below 0.01 eV˚ A-1.

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Figure S1. (a) Low and (b) high-resolution SEM images of Ce2Sn2O7 particles.

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Figure S2. (a) Low and (b) high-resolution SEM images of Ce2Sn2O7/RGO-4. (c) Low and (d)

high-resolution SEM images of Ce2Sn2O7/RGO-12.

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Figure S3. (a) Low and (b) high-resolution TEM images of Ce2Sn2O7/RGO-8.

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Figure S4. Energy-dispersive spectrometer (EDS) of Ce2Sn2O7/RGO-8.

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Figure S5. XRD patterns of Ce2Sn2O7, Ce2Sn2O7/RGO-4, Ce2Sn2O7/RGO-8 and

Ce2Sn2O7/RGO-12.

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Figure S6. The crystal structural of Ce2Sn2O7.

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Figure S7. (a) Nitrogen adsorption-desorption isotherms and (b) the corresponding pore-size

distributions of Ce2Sn2O7/RGO-8.

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Figure S8. High-resolution XPS spectra of (a) C 1s and (b) O 1s in Ce2Sn2O7/RGO-8.

The C 3d spectrum can be deconvoluted into four peaks at 284, 285, 286 and 288 eV,

corresponding to the conductive carbon, C–C (or C–H), C–O and C=O bonds.2-4 For the O 1s

spectrum, three peaks at 529.2, 531.1 and 532.9 eV are pointing to the metal-oxygen bonds,

OH- groups and the physically/chemically adsorbed water or near the surface.5,6

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Figure S9. CV curves of Ce2Sn2O7 at 0.1 mV s-1.

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Figure S10. Cycling performance of Ce2Sn2O7/RGO-8 at 2 A g-1.

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Figure S11. Rate capability of various samples at varied current densities.

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Figure S12. Nyquist plots of Ce2Sn2O7, Ce2Sn2O7/RGO-4, Ce2Sn2O7/RGO-8 and

Ce2Sn2O7/RGO-12 in fresh LIBs.

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Figure S13. (a, b) SEM images of Ce2Sn2O7 at 0.1 A g-1 after 50 cycles in LIBs.

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Figure S14. (a, b) SEM images of Ce2Sn2O7/RGO-8 at 0.1 A g-1 after 50 cycles in LIBs.

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Figure S15. (a) Relationship between the peak current and the scan rate. (b) Contribution ratio

of surface-driven and diffusion-controlled behaviors at a scan rate of 0.8 mV s−1.

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According to the CV curves at different scan rates, the contribution ratio of surface-

driven and diffusion-controlled behaviors can be calculated. The detailed calculation

process is given as following:

From Figure 5a, the power-law relationship between the current (i) and the scan rate (v) can

be described as the following Equations (S1) and (S2) (a and b are constants):7

i = avb (S1)

log(i) = blog(v) + log(a) (S2)

Based on the values of slope b, the electrochemical properties are determined. The

electrochemical behavior can be dominated by the diffusion-controlled mechanism (b value

approaches to 0.5) and the surface capacitance-dominated process (b value approaches to 1).

According to the strongest reduction and oxidation peaks, the linear relationship between the

log(i) and log(v) is obtained.

More specifically, the contribution proportion of the pseudocapacitive charge storage can be

calculated by the following Equation (S3) and (S4):

i = k1v + k2v0.5 (S3)

i/v0.5 = k1v0.5 + k2 (S4)

The i-value is composed of two parts: the pseudocapacitive effective (k1v) and diffusion-

controlled insertion (k2v0.5). According to Equation (S3), by plotting i/v0.5 versus v0.5 at different

potentials, k1 and k2 were calculated using the Equation (S4). The percentage of

pseudocapacitance can be observed using the Equation (S3) (Pseudocapacitive = k1v/(k1v +

k2v0.5)).

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The detailed calculation processes of diffusion coefficient according to electrochemical

impedance spectroscopy (EIS):

The straight line in the low frequency can evaluate the diffusion process of Li+. According

to the straight line, we could calculate the ions diffusion coefficient (D) of the Ce2Sn2O7/RGO-8

by the following Equation S5 and S6:8

Zre=Re+Rct+σω-1/2 (S5)

D=(R2T2)/(2A2n4F4C2σ2) (S6)

A is the surface area of the electrode, n is the number of electron transfer, F is the Faraday

constant, C is the molar concentration of Li+, and σ is the Warburg factor calculated from the

slope of the lines between Zre and ω-1/2.

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Figure S16. (a) Nyquist plots after different cycles. (b) Dependence of Zre on the reciprocal

square root of the frequency in the low-frequency region.

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The diffusion coefficient can be calculated according to the galvanostatic intermittent

titration technique (GITT). And the detailed calculation process is given as following:

According to Fick's second law of diffusion, the diffusivity coefficient of lithium/sodium

ions (DLi+) can be calculated based on the following equation:9

(S7)𝐷𝑁𝑎

+ =4𝜋𝜏(𝑚𝐵𝑉𝑀

𝑀𝐵𝑆 )2(Δ𝐸𝑠Δ𝐸𝑡)2

where τ is the pulse duration, mB is the mass of active material, MB is the molar mass of SnO2,

VM is the molar volume, and S is the active surface area of the Ce2Sn2O7 electrode and

Ce2Sn2O7/RGO-8 electrode. △Es and △Et can be gotten from the GITT curves. The

corresponding Li+ diffusion coefficient at different discharge/charge states of the Ce2Sn2O7 and

Ce2Sn2O7/RGO-8 in Li+ half cells can be observed using the Equation (S7).

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Figure S17. Nyquist plots of CeO2, SnO2 and Ce2Sn2O7 in fresh LIBs.

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Figure S18. (a) XRD patterns and (b) SEM image of commercial LiCoO2.

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Figure S19. (a) Schematic illustration of LiCoO2//Ce2Sn2O7/RGO-8 full cell configuration. (b)

Discharge/charge curves of LiCoO2 and Ce2Sn2O7/RGO-8 at 0.1 A g-1.

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Figure S20. (a) Discharge/charge curves and (b) cycling performance of

LiCoO2//Ce2Sn2O7/RGO-8 full cell at 0.1 A g-1.

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Figure S21. Rate capability of LiCoO2//Ce2Sn2O7/RGO-8 full cell at different current densities

(the inset shows that one coin full cell can lighten on the small car lamp).

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Figure S22. Cycling performance of Ce2Sn2O7/RGO-8//AC LICs at 0.1 A g−1.

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